The present invention relates to a method for making shelf-stable, puffed, dehydrated fruit or vegetable pieces, particularly potato pieces, using impingement drying.
Commercially available dehydrated potato pieces typically require a long time to reconstitute to a palatable texture. Such dehydration is typically performed in hot-air continuous belt dryers with relatively low air velocity which require long drying times and produce non-uniform moisture removal and product clustering.
Various approaches have been suggested for making quick-cooking dehydrated vegetable pieces having a porous structure. For example, in Eisenhardt, N. H., et al. xe2x80x9cQuick-Cooking Dehydrated Vegetable Pieces I Properties of Potato and Carrot Productsxe2x80x9d, Food Technology Vol. XVI, (5) 143-146, 1962, a method is disclosed for making porous pieces. The pieces are first partially dehydrated in a conventional manner and then heated under pressure in a closed vessel with a quick-opening lid. Then, the pieces are instantly discharged. Flashing of the water vapor within the pieces creates a porous structure. The publication states that when the entering potato pieces have a moisture content above about 53% the pieces disintegrate on instantizing and further states that the optimum moisture range is about 24-53% with optimum puffing pressures from about 30-60 psi depending on the moisture content. Subsequent work by this team and other teams at the USDA Eastern Regional Center used a battery of guns for explosion puffing into a final dryer. (J. Cording, Jr., et al. xe2x80x9cQuick-Cooking Dehydrated Vegetable Piecesxe2x80x9d Food Engineering, June 1994, 49-52) The publication suggests an optimum moisture content exiting the predrying stage of about 28-35%. Further it suggests a pressure of about 55 psi.
Another theoretical approach to making puffed potato pieces is disclosed in Brown, G. E., xe2x80x9cCentrifugal Fluidized Bedxe2x80x9d Food Technology, Dec. 23-30, 1972. In this approach dices are predried to about 40% moisture content prior to puffing. The particles rotate in a rotating basket to create centrifugal forces which when opposed by gravitational air velocity forces causes the dices to become fluidized.
Carrot pieces have been puffed commercially in a chamber maintained above atmospheric pressure but below 55 psi. When the chamber pressure is rapidly released, the carrot pieces are puffed.
Griffins et al. U.S. Pat. No. 2,705,679 discloses a method of making a dried snack potato food product by directing upwardly a hot-air stream in a duct at the bottom of a chamber through blanched diced potatoes to form a fluidized bed. The potatoes are puffed and dried to form pieces with a hollow core and a brown outer casing. The pieces rise to the top of the chamber and are removed. There is no suggestion that the dried potato dices could be rehydrated.
Adler et al. U.S. Pat. No. 3,338,724 discloses use of the same apparatus for preparing a dried, quick rehydrating puffed potato product. The process discloses immersing the potato pieces in a blanching solution of 0.1% to 2% sodium chloride solution in water.
Albisser, et al. (PCT Publication WO99/04650) discloses predrying and then puffing potato pieces for use as thin crispy snack food chips. The chips are 1.2-2.3 mm (0.047-0.090xe2x80x3) in thickness. This is typical for snack food chips. Albisser dries the chips to about 1% moisture, also typical for crisp potato chips but unsuitable for rehydratable potato pieces. The chips are coated with oil for binding seasoning. Zussman U.S. Pat. No. 5,370,898 also discloses a process for making thin snack food chip products which are predried and then puffed in an impingement dryer. As with Albisser, the Zussman product is a ready to eat, thin snack chip. The final product is a crispy snack chip (typically dried to a moisture content about 1% as set forth in Albisser).
The present invention relates to a method for making food pieces that are puffed into porous structures during impingement drying.
In particular, the method makes dehydrated, shelf-stable, puffed, vegetable or fruit food pieces, preferably ones that are rapidly rehydratable. The method includes drying moist vegetable or fruit food pieces by conveying them in a bed through an impingement drying zone maintained at substantially atmospheric pressure in which streams of pressurized heated gas in a plurality of spaced fluid conduits exit from the outlets of conduits in spaced impinging streams at a velocity in excess of about 1,000 feet per minute are directed against the moist food pieces and suspending the pieces in a fluidized bed, without applying significant centrifugal forces to the pieces. The pieces exit the impingement drying zone having a moisture content of at least about 5%. Preferably, such products have a texture and appearance suitable for use as a rapidly-rehydratable food piece. In one embodiment, the heated gas causes the moisture content of the moist food pieces to be heated and vaporized to puff them into porous pieces.
In another embodiment, the porous pieces have a moisture content in excess of about 50% (e.g. for potato pieces) on exiting said impingement drying zone. Such pieces may be further dried and packaged at a moisture content above about 4%.
The moist food pieces may be blanched prior to entering said impingement drying zone or in the zone.